The invention relates to an inhaler for products such as medicaments and particularly to an inhaler for transferring to a patient at a controlled air flow a metered dose of a medicament contained in a pressurised dispensing container.
In known metered dose inhalers, the aerosol stream from a pressurised dispensing container is fired towards a patient or user of the inhaler into a air flow travelling in the same direction. In known devices, a user inhales through a mouth piece of the inhaler and creates an air flow through the container from air inlet holes which are generally at a part of the inhaler well spaced from the mouth piece. The medicament is then released into this air flow at a point between the air inlet holes and the mouth piece so that it is travelling in the same direction as the air flow. Typically in such devices, there is no restriction in the air flow between the air inlet holes and the mouth piece. Because of this, a substantial air flow may be created by a user of the device and, because the medicament is fired into the air flow in the same direction as the air flow, the effect is that particles of medicament can attain quite substantial velocities. As inhalers of this type are normally designed to be as small as practical for the convenience of users, the distance between the point at which the medicament is fired into the air flow and the patients mouth is usually quite small so that there is little distance to reduce the inertia of the particles of medicament with the result that the particles may impact in the oro-pharynx of a user with quite high velocity. This can be a problem with some medicaments.
In an effort to overcome this problem, devices have been produced in which the medicament is fired into a holding volume which allows the velocity of the medicament to be reduced and also allows some evaporation to occur.
However, these devices with a holding volume tend to be of significantly larger size than the standard metered dose inhalers and therefore less convenient and attractive to users.
GB-A-2279879 describes an inhaler which has air inlets for allowing air into the inhaler when a user applies suction to the mouth piece. The air inlets are provided at a location axially between the air outlet of the duct means from the product container to the mouth piece, and the mouth piece, and passages are provided connecting the air inlet to a location adjacent the outlet of the duct means. In use, when a user inhales through the mouth piece, an air flow is created from the air inlet to the mouth piece, the air flow having a component directed away from the mouth piece towards the outlet of the duct means.
Such an inhaler thus allows delivery of medicament to a user at reduced velocity without significantly increasing the size of the inhaler.
Another solution to the problem would be to control the rate of air flow and the particles entrained therein.